This invention generally relates to the optical telecommunications network. More particularly, this invention relates to the support in apparatus which process lower level SONET signals for the concatenation of those lower level SONET signals into higher level SONET signals.
The telecommunications network servicing the Unites States and the rest of the world is presently evolving from analog transmission to digital transmission with ever-increasing bandwidth requirements. Fiber optic cable has proved to be a valuable tool of such evolution, replacing copper cable in nearly ever application from large trunks to subscriber distribution plants. Fiber optic cable is capable of carrying much more information than copper with lower attenuation.
While fiber optic cable represents the future in telecommunications, presently there remains an entire telecommunications network comprised of various cable types, served by equipment of different vintages, and run according to various coexisting transmission standards. While older standards, cables, and equipment will be eventually phased out, for the time being it is necessary that all the old and new standards, equipment and transmission lines be as compatible as possible. In fact, even where relatively new optical network equipment is in place, such as cross-connection (switch) equipment capable of handling SONET signals such as STS-1 signals, even higher level signals (such as STS-3 and STS-3C, details of which are seen in prior art FIGS. 6a-6d) are being generated. Typically, cross-connection equipment for such high level signals is unavailable or not commonly in place. Thus, in order for higher level signals to be utilized, mechanisms for accommodating the higher level signals to the lower level equipment are necessary; i.e., backwards compatability is required. In addition, even as apparatus for handling SONET signals such as STS-1 and STS-3 are being proposed, forward compatability is desirable, such that the same apparatus can be used to process even higher level SONET signals such as STS-12, etc.